The overall objective of this research is to determine the midbrain and medullary mechanisms which mediate binaural signals. Medical superior olivary cells responsive to low frequency sounds will be studied in the kangaroo rat. Masking-level-difference stimulus configurations will be used in order to differentiate the properties of excitatory-excitatory and excitatory-inhibitory binaural neurons. These stimuli consist of bands of noise used both as signals and maskers so that interaural level and time differences at the ears may be controlled. Cells of the inferior colliculus sensitive to high frequency sounds will be studied in the guinea pig. The purpose of this series of experiments is to determine whether this type neuron is sensitive to interaural time differences of low frequency fluctuations of the envelopes of high frequency signals. Various rates and depths of envelope modulation will be used. The stimuli to be used in both types of studies have known effects on detection and lateralization in psychophysical studies.